Multidimensional database

Multidimensional databases are variously (depending on the context) data aggregators which combine data from a multitude of data sources; databases which offer networks, hierarchies, arrays and other data formats difficult to model in SQL; or databases which offer a high degree of flexibility in the definition of dimensions, units, and unit relationships, regardless of data format.

This is an active area of database development, in which the set of desired features is somewhat vague, but better-defined than the set of known or proposed solutions. Defining and implementing a database which allows people at each level of bureaucracy and use to define tables and data formats in the way that is most useful to them, yet which supports a single clear query language and consistent infrastructure, remains (as of 2004) an open problem.

Examples: U2 suite, UniVerse and UniData; OLAP versions of many major databases, such as MDX, Oracle, and Hyperion.